1. Field of the Invention
The present invention is in the field of position tracking and machine control systems, and, more specifically, is directed to a method to calibrate hydraulic flow valves in situ.
2. Discussion of the Prior Art
A prior art four-way valve-controlled single-rod linear actuator is one of the most basic hydraulic control systems—a typical steering system. This system uses a standard four-way valve to control the output characteristics of a single-rod linear actuator. The linear actuator is typically used to generate translational output motion for hydraulic control systems. The basic construction of this actuator can be described by a simple piston-cylinder arrangement. A fixed or variable displacement pump provides an adequate hydraulic pressure power source for the valve-controlled system.
The four-way valve-controlled single-rod linear actuator can be described by using a linear equation of motion. The most practical way to enforce the control law is to use an electro hydraulic position control for the four-way spool valve coupled with a microprocessor that is capable of reading the feedback information and generating the appropriate output signal for the valve actuator.
However, when the valve dead zone (DZ) is taken into account, it results in significant nonlinearity of the four-way valve-controlled single-rod linear actuator. Therefore, the linear equation of motion for the controlled system (without dead zone) is not applicable in this non-linear situation, and can not be used to accurately predict the behavior of the nonlinear system, especially around the dead zone DZ.
The non-linear effect of the dead zone (DZ) of the quasi-proportional controller valve on the equation of motion of a non-linear system is also dependent on parameters of the non-linear system, such as friction in an actuator, friction in an implement the pump pressure response, etc.
One way to deal with this non-lineartity problem is to calibrate the entire non-linear system in situ.